10012255g spinal fusion device, bone joining implant, and vertebral fusion implant

ABSTRACT

A bone joining implant, comprising a tubular body having an open leading end and a central aperture, the central aperture similarly sized to the open leading end, the open leading end communicating with the central aperture and configured to entrap a bone projection from each of a pair of adjacent bone bodies being joined together. A method is also provided.

TECHNICAL FIELD

[0001] This disclosure relates to surgical joining of bone bodies, andmore particularly to instruments, implants and methods for instantfixation, distraction, and staged bone fusion or arthrodesis of boneodies, such as spinal vertebrae.

BACKGROUND OF THE INVENTION

[0002] This invention was specifically developed for the surgicaljoining of bone bodies, such as the fusing of contiguous spinalvertebrae so as to stabilize and prevent relative motion often resultingfrom a degenerative disc condition. Although the immediate effortleading to this disclosure is directed toward the lumbar, thoracic andcervical spine (anterior or posterior in approach), the describedvertebral implants for immediate fixation and staged stabilizationleading to arthrodesis (bone fusion) of bone bodies may be used in abone fracture or osteotomy to fuse together resulting bone bodies, andacross one or more joints or articulations. Furthermore, the implantsmay be used in the lumbar, thoracic and cervical spine.

[0003] The use of fixation plates and screws to hold together disunitedbone bodies has long been known to facilitate arthrodesis orbone-to-bone union, such as bone fusion, and healing of fractured bones.Typically, the separate bone bodies are formed when a single bonefractures, requiring bone reunion. Plates are secured across a fractureregion with screws, joining together the bone bodies. The plates holdthe bone bodies together in proximate relation, facilitating bone growthand fusion therebetween. In this manner, the bone bodies are supportedin close proximity, or in direct contact which facilitates fusiontherebetween. For cases where it is impossible to fixture together bonebodies internally of a patient's skin, external fixation is used. Forexternal fixation, threaded pins are rigidly secured into each bonebody. The pins, which extend outwardly of a patient's skin, are fixturedtogether with an external fixation device, placing the bone bodies inadjacent proximate position to promote healing therebetween. However,these techniques are not practical for certain joints such as jointsformed between spinal vertebrae. Therefore, a significant number ofstabilizing implants have been designed for joining together contiguousvertebrae.

[0004] One early technique for achieving arthrodesis between adjacentvertebrae across a joint or articulation is the well-known ClowardTechnique for use in the human cervical spine. A solitary dowel of boneis tapped into place in a prepared circular bed that is smaller than thedowel of bone. The dowel acts as a wedge, distracting the surroundingsoft tissues of the joint, and separating the bone bodies or vertebraejoined there along. The intervertebral disc substantially comprises thesoft tissues of the joint. The dowel of bone is inserted, or wedged intoplace, providing its own stability by putting an annulus of the disc onstretch. Additionally, simple friction of the inserted dowel betweenadjacent vertebral bodies stabilizes axial dislocation. However, asecond surgical procedure must be performed to extract or harvest thedowel of bone, substantially adding trauma to the procedure, increasingcosts, as well as increasing the threat of infection to the patient.Alternatively, bank bone from human donors can be used, but bank bone isless osteogenic and may introduce infection, or even transmission ofAcquired Immune Deficiency Syndrome (AIDS) or hepatitis. Furthermore,bone morphogenic protein, hydroxy apatite, or other bone stimulatingmaterial may be utilized. Additionally, there has been a need to ensurethe implant remains axially secured which has lead to furtherdevelopments.

[0005] A step forward from the Cloward Technique was provided by Bagby(U.S. Pat. No. 4,501,269) wherein a metal dowel uses the same principle.A perforated cylindrical hollow implant is inserted between preparedsurfaces across a vertebral joint. The inserted implant immediatelystabilizes the joint by spreading the bony surfaces apart in wedgedopposition to surrounding tissue. This initial stabilization is moresubstantial because a metal dowel, unlike a bone dowel, will not beabsorbed or fatigue in use. Over time, fusion occurs through and aroundthe implant which is filled with bone fragments. Use of the metal doweleliminates the need for a second operation to harvest a dowel of bone.Bone fragments to be inserted in the implant are retrieved duringpreparation of the circular beds in each vertebra. Furthermore, such ametal implant avoids the disadvantage of having to use bone bank toobtain donor bone. The Bagby implant described in U.S. Pat. No.4,501,269 has a smooth outer surface, interrupted only by numerousopenings or fenestrations through which bone ingrowth and through growthcan occur. Ends of the implant are substantially closed, with one endreceiving an end cap such that bone fragments are contained therein.Bone morsels or bone grafts are typically harvested when preparing thecircular bed in each vertebra, after which they are placed into thefenestrated metal cylindrical implant. The Bagby implant is then drivenor tapped into place in a manner similar to the placement of Cloward'sBone Dowel, which was solely directed for use in the cervical spine.However, the original Bagby implant relies completely upon stretch ofthe annulus to stabilize the vertebrae during bone remodeling andfusion.

[0006] Improvements have also been made to “Cloward's Technique” whereintwo dowel bone grafts are posteriorly inserted (Wiltberger's Technique)between adjacent lumbar vertebral bodies. Furthermore, threaded surfaceshave been added to such bone grafts in order to keep the grafts in place(Otero-Vich German Application Ser. No. 3,505,567, published Jun. 5,1986). More recently, a number of U.S. Patents have proposed combiningthe threaded features from threaded bone grafts with a metal implant,resulting in rigid threaded implant structures for placement betweenadjacent spinal vertebrae.

[0007] One threaded metal fusion implant disclosed in Michelson (U.S.Pat. No. 5,015,247) provides a cylindrical fusion implant having anouter diameter sized larger than the space between adjacent vertebrae tobe fused. Threads provided on the exterior of the member engage thevertebrae to axially secure the implant therebetween. The implant has aplurality of openings configured along the cylindrical surface topromote bone ingrowth. However, the threads per se of the implant do notfunction as a fastener to fix together the adjacent vertebral bodies.Instead, the implant functions as a wedge, imparting a distraction forceacross the disc which stabilizes the articulation formed therebetween bystretching the annulus of the disc. In fact, the threaded implant reliessolely on the annulus to provide stabilization between the vertebrae, indirect response to wedge-induced distraction created therebetween.Distraction of the annulus stabilizes the two vertebrae, enablingingrowth to later occur within the implant. Therefore, through-growthand fusion (arthrodesis) occur between the adjacent vertebrae subsequentthereto depending on the immobilizing potential of an intact healthyannulus which may or may not be present.

[0008] Several additional problems result from the provision of threadson a cylindrical fusion implant. One problem results in that threadstake up additional space which makes implantation in areas havinglimited anatomical space very difficult, such as in the posteriorapproach in the lumbar spine. Additionally, the threads effectively makethe wall thickness greater which further separates bone provided insidethe implant with bone provided outside the implant, which can delayinitial bone union.

[0009] For bone fusion to occur with any of the above devices, theinvasion of new delicate blood vessels from the adjacent healthy bone isnecessary for the creation of new living interconnecting bone. Wherecomplete stabilization does not occur instantaneously upon implantation,motion can disrupt the in growth of delicate blood vessels. Disruptionof the vessels then restricts or even prevents bone healingtherebetween. The same problem occurs with any of the above mentionedimplant techniques, including the threaded techniques of Otero-Vich andMichelson. Even when the annulus is completely on stretch, the threadsper se of these constructions do not function in the manner ofconventional screws, extending through one object and into another.Namely, they do not function to fasten together adjacent bodies bycoaction of the implant with each body. For example, the threads merelyact as a series of ridges that engage with each adjacent bone body,while the implant body functions as a wedge. The implant distracts apartthe vertebral bodies which stretches the annulus, and stabilizes thearticulation as a consequence thereof, while the thread functions solelyto prevent axial dislodgement. Furthermore, the presence of threadsrequires the implant to be screwed in place via a torquing process,instead of tapping the implant directly into position.

[0010] Hence, some recent designs have resulted in an implant thatproduces immediate fixation per se between bone bodies followinginsertion and independent of the annulus. Such designs show promiseparticularly for cases where the annulus structure is substantially orcompletely weakened or damaged at surgery. Where the annulus is damagedso significantly_as to lose structural integrity, the wedge-effect ofprior art threaded implants will not produce any distraction forcesacross the annulus. Also, when the implant is used to arthrodese andchange angulation, a healthy annulus cannot be totally corralled to beplaced on stretch. As a result, there is no form of stabilization orfastening between bone bodies sufficient to enable the occurrence ofarthrodesis therebetween when the annulus is weakened or inadequate.Additionally, there exist additional shortcomings with such recentdesigns as discussed below.

[0011] One such design that produces immediate fixation is disclosed inBagby (U.S. Pat. No. 5,709,683) as a bone joining implant having aspline or undercut portion that engages in assembly with each bone bodyto be joined. However, such design requires the preparation of bone bedsthat are engaged in interlocking relation with a bone bed engagingportion provided by such undercut portions.

[0012] Many of the previously described implants can be inserted betweenvertebrae while such vertebrae are distracted with a distraction tool.One such tool uses a threaded pin which is inserted laterally into eachbone body, with such pins being rigidly secured therein. Such tooldistracts the vertebrae by separating the pins and vertebrae whichstretches the annulus. A drill is then used to drill out bone bedswithin the vertebrae, after which the implant is inserted therein.However, such procedure does not always impart sufficient distractionand takes time and space to implement.

[0013] Yet another group of implant designs provide distraction betweenadjacent vertebrae, including U.S. Pat. No. 5,665,122 to Kambin and U.S.Pat. No. 5,702,455 to Saggar. Kambin teaches an expandableintervertebral implant formed from several components that cooperatewith an expansion screw to distract adjacent vertebral bodies byexpanding two of the cage components relative to one another. However,such design is formed from several discrete components that are movablyfastened together and which are susceptible of loosening andmisadjusting within a patient. Saggar teaches a spine stabilizingprosthesis that is inserted within a cavity between vertebrae. Suchdesign forms a jacking screw adjustment member that expands apart a pairof bearing members, each engaged with a respective vertebra. However,such design is illustrated in use as being inserted within a vertebralcavity that is formed by removal of a portion of a vertebra such as isformed by a corpectomy.

[0014] Therefore, there is a present need to provide an implant devicethat instantly fastens bone bodies together upon implantation, enhancesarthrodesis by encouraging bony fusion adjacent the implant, and impartsdistraction between adjacent bone bodies during insertion. There is alsoa need to provide such a device that facilitates staged stabilizationleading to bone fusion, in a manner that is relatively simple, morereliable, less complicated, has fewer parts, and leads to quicker andmore thorough bone fusion and remodeling therebetween. The final stageof bone fusion through and around the implant substantially eliminatesany need for the implant to maintain the fusion, thus allowing the boneunion to provide primary support therebetween.

SUMMARY OF THE INVENTION

[0015] In accordance with one aspect of the invention, a bone joiningimplant comprises a tubular body having an open leading end, an opentrailing end, and a central aperture; the open leading end communicatingwith the central aperture and configured to entrap a bone projectionfrom each of a pair of adjacent bone bodies being joined together. Thebone projection is integrally formed from each bone body being joined,and the implant houses bone graft material therein. The bone projectionsand bone graft material cooperate to enhance arthrodesis. Such implantdirectly and instantly stabilizes adjacent bone bodies by entrapping thebone projections.

[0016] In accordance with a second aspect of the invention, a vertebralinterbody implant comprises a tubular body having an oblique outersurface and a cylindrical inner surface, and a tapered portion extendingfrom a cylindrical leading end between the inner surface and the outersurface. The cylindrical leading end is sized to be received within bonebeds of adjacent vertebrae being joined, and the tapered portionoperative to self-distract the vertebrae during insertion of the obliqueouter surface therebetween. The tapered portion, in combination with theoblique outer surface, imparts indirect stabilization by commanding anannulus between the adjacent bone bodies to tighten or stretch inresponse to distraction of the adjacent bone bodies.

[0017] In accordance with a third aspect of the invention, a tubularimplant contains an aperture extending completely through the implanthaving a substantially continuous inner diameter which facilitates x-rayevaluation of bone healing within the implant, following implantationand arthrodesis. Particularly, such aperture facilitates evaluationextending in a direction along the axis of the tubular implant,generally in an anterior to posterior direction.

[0018] In accordance with a fourth aspect of the invention, a singletubular body implant is provided for implantation between the pair ofbone bodies. Such tubular implant caters to a reduced amount of surgeryin that a single implant serves the surgical purpose of two implants, inselected cases.

[0019] In accordance with a fifth aspect of the invention, a tubularimplant includes a tubular body having an oblique outer surface and acylindrical inner surface that is configured to be received inconforming implantable relation with a pair of bone bodies that areformed from a single cylindrical cut taken between adjacent bone bodies.Upon distraction, the cylindrical cut forms an obliquity between theadjacent bone bodies which conforms in substantially compliant fit-upwith the oblique outer surface of the tubular implant. Such conformingfit-up increases frictional stabilization between adjacent bone bodiesby generating a larger contact surface area therebetween. Furthermore,the oblique outer surface mates with such bone bodies in a manner thatimparts a degree of lateral stabilization so as to prevent lateralmovement at the adjoining interfaces.

[0020] In accordance with a sixth aspect of the invention, a tubularimplant is provided with an open leading end and a central aperture in amanner to entrap intact bone projections extending from each of a pairof adjacent bone bodies. Such entrapment provides immediate, or instant,fixation between the adjacent bone bodies in a manner that caters toretention of the local bone bodies via the intact bone projections.Furthermore, bone graft material, or chips, are provided within theinterior of the tubular implant so as to provide osteogenic materialthat is placed inside the implant. Such osteogenic material ispreferably generated during preparation of the bone beds, whicheliminates the need to perform additional surgeries for obtainingforeign bone graft material from other locations on a patient, or fromanother patient.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

[0022]FIG. 1 is a perspective view of a vertebral structure showing avertebral interbody implant embodying this invention;

[0023]FIG. 2 is a perspective view of a vertebral structure showing apair of vertebral interbody implants, similar to the implant depicted inFIG. 1, embodying this invention;

[0024]FIG. 3 is a simplified frontal view illustrating a pair ofadjacent vertebral bodies prepared with distraction pins;

[0025]FIG. 4 is a simplified frontal view corresponding to the viewdepicted in FIG. 3, and illustrating a pair of adjacent vertebral bodiesdistracted by a distraction tool (not shown) that applies forces to thedistraction pins;

[0026]FIG. 5 is a perspective view of a pair of adjacent vertebrae andillustrating a drill guide and drill bit used to form a first bore usedto prepare bone beds within the vertebrae;

[0027]FIG. 6 is a perspective view of the pair of vertebrae of FIG. 5,and illustrating a hole saw used with the drill guide to further preparethe bone beds within the vertebrae by cutting a cylindrical kerftherein;

[0028]FIG. 7 is a simplified side view illustrating the hole saw of FIG.6 cutting a cylindrical kerf within the pair of vertebrae;

[0029]FIG. 8 is a perspective view of an alternative hole saw usablewith a power tool for cutting a cylindrical kerf within the vertebralbodies of FIG. 7;

[0030]FIG. 9 is a simplified sagittal view illustrating the alternativehole saw usable with a power tool of FIG. 8 cutting a cylindrical kerfwithin the pair of vertebrae;

[0031]FIG. 10 is a perspective view of a kerf cleaning/deburring toolfor cleaning debris from the cylindrical kerf formed within thevertebral bodies;

[0032]FIG. 11 is a simplified sagittal view showing the kerfcleaning/deburring tool of FIG. 10 and illustrating the removal ofdebris from within the cylindrical kerf formed within the vertebralbodies.

[0033]FIG. 12 is a perspective view of the vertebral interbody implantof FIG. 1 for insertion within the prepared bone beds of FIG. 11;

[0034]FIG. 13 is a perspective view taken from the driven end of thevertebral interbody implant of FIG. 12;

[0035]FIG. 14 is a side view of the vertebral interbody implant of FIG.12;

[0036]FIG. 15 is a leading end view of the vertebral interbody implantof FIG. 12;

[0037]FIG. 16 is a driven end view of the vertebral interbody implant ofFIG. 12;

[0038]FIG. 17 is an unrolled plan view of the outer peripheral surfaceof the vertebral interbody implant of FIGS. 12-16;

[0039]FIG. 18 a perspective view illustrating an implant insertion toolusable for inserting the implant of FIGS. 12-16;

[0040]FIG. 19 is a simplified frontal view illustrating a pair ofvertebrae that have bone beds prepared according to the steps depictedin FIGS. 1-11 comprising a cylindrical kerf;

[0041]FIG. 20 is a simplified frontal view illustrating the vertebrae ofFIG. 19 in a distracted position corresponding to the position generatedby inserting the implant of FIGS. 12-16;

[0042]FIG. 21 is a simplified frontal view illustrating the vertebrae ofFIG. 20 in a distracted position caused by inserting Applicant's implantof FIGS. 12-16;

[0043]FIG. 22 is a simplified sagittal view taken along the centerlineof the implant of FIGS. 12-16;

[0044]FIG. 23 is a surgical time simplified sagittal view of the implantof FIG. 22 received within the prepared bone beds of adjacent vertebraeand containing bone fragments immediately following implantation;

[0045]FIG. 24 is a healed time simplified sagittal view of the implantof FIG. 22 received within the prepared bone beds of adjacent vertebraeand illustrating the vertebra following bone remodeling andreorganization and showing arthrodesis;

[0046]FIG. 25 is a coronal view of the implant and healed bonecomprising vertebrae and taken along line 25-25 of FIG. 24 and showingarthrodesis;

[0047]8FIG. 26 is a perspective view of an alternatively constructedvertebral interbody implant similar to the embodiment depicted in FIGS.1-25 for insertion within the prepared bone beds of FIG. 11; and

[0048]FIG. 27 is a frontal view of the vertebral interbody implant ofFIG. 26.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] This disclosure of the invention is submitted in furtherance ofthe constitutional purposes of the U.S. Patent Laws “to promote theprogress of science and useful arts” (Article 1, Section 8).

[0050] A preferred embodiment bone joining implant in accordance withthe invention is first described with reference to FIGS. 1, 12-18 and21-25. Such an implant is described further below with respect to anopen-ended vertebral interbody implant having instant fixation in theform of a leading open end and self-distraction features in the form ofa cylindrical inner surface and an oblique outer surface. The fixatingand self-distracting implant is designated in FIGS. 1, 12-18 and 21-25generally with reference numeral 10. An alternative implementationcomprising a pair of somewhat smaller sized implants 110 are depicted inFIG. 2. Yet another alternative implementation comprises a substantiallycylindrical tubular implant 210 depicted in FIGS. 26 and 27.

[0051] As shown in FIGS. 1, 12-18 and 21-25, implant 10 comprises arigid, unitary body having a cylindrical leading edge 86 and an obliqueouter surface 90, with an open leading end 96 (see FIGS. 12-16). Asshown in FIG. 1, implant 10 is inserted within an aperture 18 formedbetween a pair of adjacent vertebral bodies 12 and 14 within a vertebralcolumn 16.

[0052] As shown in FIG. 1, aperture 18 is prepared within vertebralbodies 12 and 14, and disc 16, according to the procedure and toolsdepicted in FIGS. 5-11 described below in further detail. Aperture 18forms a pair of vertebral bone bodies 22 and 24 that are formed to havea cylindrical configuration comprising a cylindrical kerf 158 (see FIG.19). A leading cylindrical end of implant 10 is inserted into aperture18, causing annulus 20 to distract as implant 10 is inserted therein(see FIGS. 19-21 below). A leading open end 96 (see FIG. 12) of implant10 entraps an intact living bone projection 168 and 170 on eachrespective vertebral body (see FIGS. 19-22) which imparts immediatefixation between adjacent vertebral bodies 22 and 24 upon implantation.

[0053] More particularly, vertebrae 12 and 14 comprise neighboring bonebodies of a vertebral column 16 (see FIG. 1). A resilient articulationor joint is formed between vertebra 12 and 14 by a disc 16 extendingbetween vertebrae 12 and 14. Anatomically, the disc is made up of acentral nucleus pulposus and an outer encircling annulus. The annulusand nucleus pulposus are composed of laminae of fibrous tissue andfibro-cartilage. The nucleus pulposus, located at the center of thedisc, comprises a soft, pulpy, highly elastic substance. The annulus isformed from laminae of fibrous tissue extending in criss-crossingfashion to encircle the nucleus pulposus. Additionally, theintervertebral disc is adherent, by its cephalad and caudad surfaces, toa thin layer of hyaline cartilage that covers the top and bottomsurfaces of adjacent vertebrae. In a healthy patient, adjacent vertebra12 and 14 are spaced apart by disc 16. However, degenerative discdisease and localized trauma can cause degradation or complete loss ofthe soft tissue components between neighboring vertebrae. For example,the annulus can partially or completely tear which can seriously degradethe structural condition of the articulation. Additionally, fluid canescape from the nucleus pulposus. When any of the above happens,vertebrae 12 and 14, loaded by the normal weight bearing of a patient,are pressed into closer adjoining positions, which can result inpinching of nerves that extend from between vertebrae of the spinalcolumn (not shown).

[0054] Therefore, there is a need to recover the disc spacing providedby a normal healthy disc 20 by way of inserting implant 10. Furthermore,there is a need to provide implant 10 with a fixation that instantlyinterlocks adjacent vertebra 12 and 14 together upon being implanted.Furthermore, there is a need for such an implant 10 that impartsdistraction to disc 20 upon insertion and that facilitates stagedstabilization resulting in arthrodesis to occur between the vertebralbodies, following initial implantation. Even furthermore, there is aneed to instantly fix adjacent vertebrae together since relative motioncan otherwise cause pinching of nerve tissue.

[0055] As a result, implant 10 can be inserted, preferably in a centrallocation between adjacent vertebrae 12 and 14 of patients who have bad,ruptured or degenerative discs. A pair of somewhat smaller sizedlaterally positioned implants may also be used in chosen cases, as shownin FIG. 2. Furthermore, implant 10 can be axially oriented anterior toposterior, or even laterally. In summary, implants 10 are adapted forimplantation between prepared bony surfaces or beds 22 and 24 and acrossthe articulation formed by disc 20. A typical implantation might involveplacement of one or more implants 10 as required in order to stabilizeand fix the joint during bone ingrowth and through-growth of the implantstructure. Bone growth is also accomplished outside of and surroundingthe implant.

[0056]FIG. 2 illustrates an alternative implementation comprising a pairof laterally positioned implants 110. Implants 110 are essentiallyidentical to implant 10 (of FIG. 1), but are sized smaller in dimension.Such implementation enables correction of lateral spinal curvatures byinserting a laterally positioned pair of implants 110 having differentouter dimensions into similarly sized bone beds between adjacentvertebrae. Such dual implant implementation also imparts additionalstability across disc 20 over that provided by the single implantimplementation depicted in FIG. 1.

[0057] However, such dual implant implementation uses individualimplants 110 that are sized smaller than the single implant 10 ofFIG. 1. As a result, such dual implant implementation uses smaller sizedapertures 118 which do not invade as much cancellous bone as theapertures 18 (see FIG. 1) for the larger sized single implantimplementation of FIG. 1. A solitary implant 10 as shown in FIG. 1invades cancellous bone since aperture 18 has a larger diameter. Incontrast, the smaller sized dual implants 110 of FIG. 2 tend to invademostly cortical bone on the end plates. However, cancellous bone is moredesirable for bone growth during staged bony fusion since cancellousbone is more osteogenic than cortical bone. New growth bone, or callusbone, comprises soft cancellous bone that only becomes hard (cortical)over time via action of Wolff's Law of maturity.

[0058]FIGS. 3 and 4 illustrate one technique for distracting anarticulation between adjacent vertebral bodies 12 and 14 by placing disc20 under stretch. Such technique has been used with prior art vertebralinterbody implants and fusion cages to impart distraction, after whichan aperture 218 (see FIG. 3) is formed in the articulation into which animplant is inserted. However, some relaxation typically occurs to disc20 following insertion.

[0059] In contrast, Applicant's implant depicted in FIGS. 1 and 2generates self-distraction during insertion. It is understood thatApplicant's invention can be implemented in combination with thedistraction technique taught in FIGS. 3 and 4 in order to further impartdistraction between vertebral bodies 12 and 14 by stretching disc 20.

[0060] As shown in FIG. 3, a rigid metal pin 26 and 28 is inserted in alateral direction into each vertebra 12 and 14, respectively. Pins 26and 28 are each formed from a cylindrical piece of rigid stainless steelhaving a threaded leading end (not shown). Such pins 26 and 28 areformed in a manner similar to Harrington rods, but are shorter inoverall length. Pins 26 and 28 are threaded into respective aperturesthat have been pre-cut or drilled into vertebrae 12 and 14,respectively. Preferably, pins 26 and 28 are inserted laterally intovertebrae 12 and 14 such that pins 26 and 28 are rigidly secured inparallel respective relation separated by a spaced apart distance D₁.

[0061] As shown in FIG. 4, external distraction force is applied betweenpins 26 and 28 by a distraction tool (not shown) so as to impartdistraction between pins 26 and 28 and vertebral bodies 12 and 14.Several tools are understood in the art for distracting apart vertebralbodies. One technique involves modifying a pair of forceps to receivepins 26 and 28. U.S. Pat. No. 4,898,161 to Grundei teaches anothervariation of a distraction tool comprising a pair of forceps for pushingapart vertebrae. According to the Grundei tool, pins are integrallyformed by the forceps for pushing apart adjacent vertebrae when jaws onthe forceps are spread apart. Such U.S. Pat. No. 4,898,161 is hereinincorporated by reference as showing a distraction tool presentlyunderstood in the art. Preferably, pins 26 and 28 are moved apart by thedistraction tool so that they remain in parallel relation. Accordingly,vertebral bodies 12 and 14 are moved apart without imparting anyrelative rotation therebetween. As a result, pins 26 and 28 aredistracted to a new spaced apart distance D₂. Hence, vertebral bodies 12and 14 are distracted apart a total distance D_(T)=D₂−D₁.

[0062] Following distraction of vertebral bodies 12 and 14, an aperture218 is formed cooperatively within vertebral bodies 12 and 14 andfurther within disc 20 with a drill bit and/or saw. Such aperture 218forms a pair of bone beds 222 and 224 that receive a prior art vertebralinterbody implant.

[0063] Optionally, an aperture 18 (as depicted in FIG. 19) can be formedwithin vertebral bodies 12 and 14 of FIG. 4. Accordingly, distractionD_(T) can be imparted between vertebral bodies 12 and 14 which is inaddition to the self-distraction that is generated by merely insertingimplant 10 of Applicant's invention between bodies 12 and 14 asdescribed below with reference to FIG. 21.

[0064] FIGS. 5-11 illustrate the preparation of aperture 18 and bonebeds 22 and 24 within vertebral bodies 12 and 14, respectively (of FIG.1). Such figures illustrate one technique for preparing a suitable pairof bone beds within adjacent vertebrae 12 and 14 for receiving implant10 (of FIG. 1) such that self-distraction and immediate fixation areimparted between vertebral bodies 12 and 14.

[0065]FIG. 5 depicts a tool guide 30 and a drill bit 38 that are used todrill a bore 40 (see FIGS. 6 and 7) into vertebral bodies 12 and 14 anddisc 20. Bore 40 is drilled a sufficient depth into bodies 12 and 14 soas to leave intact living bone projections 168 and 180 (see FIG. 11)having sufficient size to impart instant fixation between bodies 12 and14 upon insertion of implant 10.

[0066] As shown in FIG. 5, tool guide 30 is first tapped into engagementwith vertebral bodies 12 and 14 by an alignment drive and hammer (notshown). Sharp fingers or projections 32-35 engage and enter the outersurfaces of bodies 12 and 14 which causes tool guide 30 to be rigidlyand securely seated between bodies 12 and 14. In this position, acentral bore 36 of tool 30 is aligned in an anterior/posteriordirection. Bore 36 is sized to receive and guide a tool bit 38 in ananterior/posterior direction through bodies 12 and 14 and annulus 20.

[0067] More particularly, drill bit 38 is driven in rotation by a drill(not shown) so as to cut out bore 40 (see FIG. 7). One suitable drillcomprises a Hudson hand-driven manual drill. Alternatively, a powerdrill can be used to drive drill bit 38. Typically, bore 40 is drilledwith sufficient depth into bodies 12 and 14 to extend between 30-70% ofthe depth of cylindrical kerf 44 as shown in FIG. 7. Kerf 44 issubsequently cut using one or more of the tools depicted with referenceto FIGS. 6-11 as described below.

[0068]FIG. 6 illustrates a hole saw 42 used in combination with toolguide 30 to form part or all of a cylindrical kerf 44 (see FIG. 7). Asillustrated in FIG. 7, hole saw 42 is used to cut a cylindrical groove68 (see FIG. 9) to a depth approaching 90% of the finished depth of kerf44. Hole saw 42 is inserted into bore 40 such that a cylindrical grooveis cut in axial alignment with bore 40. Thereafter oscillatingcylindrical blade 50 (of FIGS. 8 and 9) is used to cut the remainingdepth of cylindrical groove 70 which corresponds to the final depth ofkerf 44 as shown in FIG. 9. A hand-driven kerf cleaning/deburring tool72 is then used to clean debris 84 (see FIGS. 10 and 11) fromcylindrical groove 70 which prepares and finishes kerf 44 therein.Optionally, hole saw 42 (of FIGS. 6 and 7) and/or oscillatingcylindrical blade 50 can be used to prepared kerf 44. Furtheroptionally, kerf 44 can be formed solely by use of hand-driven tool 72.

[0069] As shown in FIGS. 6 and 7, hole saw 42 comprises a hollow sawblade having a shank that is driven in rotation by a drill (not shown).The cylindrical saw blade of hole saw 42 is inserted in bore 36 of toolguide 30 during a cutting operation. Guide 30 directs hole saw 42 to cutin an accurate anterior/posterior direction that is coaxial with bore 40formed by drill bit 38 (of FIG. 5).

[0070]FIG. 7 illustrates hole saw 42 during a cutting operation.According to one implementation, hole saw 42 is used to cut to a depthindicated by cylindrical groove 68 shown in FIG. 9. Subsequently,reciprocating cylindrical blade 50 (of FIGS. 8 and 9) is used to furtherand substantially form a remaining portion of kerf 44.

[0071]FIG. 8 illustrates one suitable construction for a reciprocatingcylindrical blade 50 used in conjunction with hole saw 42 (of FIGS. 6and 7) and tool 72 (of FIGS. 10 and 11) to form cylindrical kerf 44.More particularly, cylindrical blade 50 comprises a speciallyconstructed reciprocating blade designed for use with an existing, orslightly modified, Stryker hand-held saw 46. Several Stryker hand-heldsaws are commercially available for producing reciprocating saw blademotion. Stryker Corporation is located in Kalamazoo, Mich., anddevelops, manufactures, and markets speciality surgical instruments.

[0072] As shown in FIGS. 8 and 9, cylindrical blade 50 comprises ahollow cylindrical metal tube with a leading end forming a plurality ofcutting teeth 62, and a trailing end forming an end wall 63. End wall 63of FIG. 9 contains a pair of small apertures 64 positioned above a pairof enlarged apertures 66. Apertures 64 and 66 are sized and positionedin end wall 63 so as to mount cylindrical blade 50 coaxially about theaxis of rotation generated by saw blade drive member 48 on Stryker saw46. Pins 56 and 58 interdigitate with apertures 64 and 66, respectivelyto impart rotatable securement between blade 50 and drive member 48. Athreaded hexagonal fastener 52 is received through a bore 65 in end wall63 and into a complementary threaded aperture 60 within drive member 48so as to rigidly secure blade 50 onto drive member 48 for reciprocation.

[0073] In operation, drive member 48 is driven in reciprocating pivotalmovement by saw 46, which imparts reciprocation to blade 50 and teeth 62so as to generate cutting forces. Such cutting forces are directedagainst an object such as vertebral bodies 12 and 14 and disc 20 asshown in FIG. 9. Cylindrical blade 50 is sized with a dimension close tothat of bore 36 of tool guide 30 such that saw blade 50 is axiallyguided in coaxial relation within bore 40 (see FIG. 7) and cylindricalgroove 68 (see FIG. 9). Cylindrical blade 50 is used to cut all the wayfrom groove 68 and to groove 70 which is substantially the entire depthof the finished kerf 44 (of FIG. 11).

[0074]FIG. 10 illustrates one construction for a kerf cleaning/deburringtool 72 used to remove debris 84 from within cylindrical groove 70 ofvertebral bodies 12 and 14 (see FIG. 11). Tool 10 includes a t-shapedhandle 74 and a hollow cylindrical cutting body 76 having an open endterminating in a plurality of circumferentially spaced apart cuttingteeth 78. A deep gullet, or throat, 82 is provided between adjacentteeth 78 for collecting debris that is removed when tool 10 is insertedand rotated within cylindrical groove 70 (see FIG. 11).

[0075]FIG. 11 shows tool 72 in partial breakaway view positioned toclean out debris 84 from cylindrical groove 70. Tool 72 is inserted intogroove while handle 74 is rotated back and forth to impart back andforth rotary movement to teeth 78 within groove 70. Debris 84 is removedand cut from groove 70 by movement of teeth 78. Such debris 84 lodges ingullets and within the hollow interior of body 76. Tool 72 is thenremoved from groove 70 which also removes debris 84. Furthermore, teeth78 impart a final finished dimension to cylindrical kerf 44 prior toinserting an implant therein.

[0076]FIG. 12 illustrates self-distracting and fixating implant 10 inperspective view. Implant 10 has a cylindrical leading edge 86 and atrailing edge 88. An oblique outer surface 90 and a cylindrical innersurface 92 are formed between edges 86 and 88. A central cylindricalchamber, or aperture, 94 is formed within implant 10, between edges 86and 88. Chamber 94 forms an open leading end 96 and an open trailing end98 within implant 10. Upon implantation, open leading end 96 entrapsprojections 168 and 170 as shown in FIGS. 21 and 22 which impartsimmediate fixation between vertebral bodies 12 and 14.

[0077] As shown in FIG. 12-17, four discrete beveled retaining tabs 116are formed on oblique outer surface 90 adjacent to trailing end 88. Tabs116 are positioned about surface 90 so as to engage within one of thebone beds formed in the vertebral bodies being joined. Such fingers havea ramped front face and a sharp rear edge that serves to facilitateinsertion of implant 10 between prepared bone beds, while preventingdislodgement therefrom. More particularly the sharp rear edges of tabs116 serve to engage with such bone beds, preventing inadvertentdislodgement of implant 10 from between a pair of prepared bone beds.

[0078] As shown in FIGS. 12-15 and 17, a plurality of interruptions 102are formed in cylindrical leading edge 86, and extending into a taperedportion 104. Such interruptions comprise wedge-shaped removed portionsof tapered portion 104 which cooperate to form individual taperedfingers 100 extending from cylindrical leading edge 86. Interruptions102 serve to further collect any debris that still remains withincylindrical kerf 44 during insertion as shown in FIG. 22.

[0079] Also shown in FIGS. 12-15 and 17, a plurality of fenestrations112 are provided spaced apart and extending through the tubular wall ofimplant 10. Such fenestrations 112 serve to facilitate bony ingrowth andthrough growth, and generally staged fusion as discussed in Applicant'sissued U.S. Pat. No. 5,709,683 incorporated herein by reference.Additionally, a pair of slightly larger sized tool fenestrations 114 areprovided along trailing edge 88 for receiving pins 144 and 146 of aninsertion tool 120, as shown and described in greater detail below withreference to FIG. 18. Tool fenestrations 114 are positioned at locationsperpendicular to guide slots 106 and 108; namely, at the 3 o'clock and 9o'clock positions. During insertion, guide slots 106 and 108 are used tovisual guide placement of implant 10 so as to impart self-distraction toadjacent vertebral bodies, as described in further detail below.

[0080] Such bony ingrowth and through-growth occur following insertionof implant 10 within bone beds defined by inner surfaces 160 and 164 andouter surfaces 162 and 166 as shown in FIG. 23. More particularly,remodeled bony ingrowth and through-growth are shown and described belowin FIGS. 24 and 25. Fenestrations 112 extend substantially throughoutthe walls of tubular implant 10, particularly as shown in FIG. 17. Suchfenestrations 112 offer avenues of ingrowth of bone between vertebrae,which is stimulated by bone graft material placed within a centralchamber comprising cylindrical aperture 94 (see FIG. 15). In thismanner, fenestrations 112 serve to facilitate earlier and more thoroughingrowth of bone within implant 10. Furthermore, fenestrations 112enhance overall through growth of bone through implant 10.

[0081] A pair of guide slots 106 and 108 are also provided on a trailingend 88 of implant 10 to facilitate proper presentation and alignmentwhen inserting implant 10 between a pair of vertebral bodies. Guideslots 106 and 108 are positioned at the 12 o'clock and 6 o'clockpositions during insertion, corresponding with superior and inferiorlocations. Such positioning is crucial since implant 10 has an obliqueouter surface that is designed to impart distraction between adjacentvertebra during insertion therebetween.

[0082] According to FIG. 17, oblique outer surface 90 of implant 10 isshown in an unrolled plan view to better depict layout of fenestrations112, tool fenestrations 114, fingers 100, tabs 116 and guide slots 106and 108. Tapered portion 104 is also shown extending along leading edge86. Guide slots 106 and 108 are shown positioned along opposite trailingedge 88.

[0083] One feature of Applicant's invention is provided by forming acylindrical leading edge 86, and an oblique outer surface 90. Edge 86 isinserted into an appropriately sized cylindrical kerf 44 (see FIG. 21),and insertion pressure is applied sufficient to generate distractionbetween adjacent vertebrae as leading tapered portion 104 is insertedtherein. Hence, vertebrae 12 and 14 are distracted followingimplantation of implant 10 therebetween.

[0084]FIG. 18 illustrates an insertion tool or instrument 120 configuredfor loading implant 10 into prepared bone beds formed by kerf 44 andbore 40 (see FIG. 11). More particularly, bone beds are provided by apair of inner surfaces 160, 164 and a pair of outer surfaces 162, 166formed at least in part by kerf 44 as viewed in FIGS. 19 and 20.

[0085] Insertion tool 120 is formed from a driver 122 and a guide 124.Guide 124 forms a threaded bore 125 in which driver 122 is received inadjustable, threaded engagement via threaded portion 150 of driver 122.An adjustment nut 126 cooperates with a lock nut 126 to enablesecurement of driver 122 within guide 124 at a desired, threaded axiallocation.

[0086] Once driver 122 has been threaded sufficiently into guide 124 tocause pins 140 and 142 to be moved outwardly via contact with end 148,nut 126 is tightened into engagement against trailing end 138.Subsequently, lock nut 128 is tightened into engagement against nut 126.

[0087] A recessed mounting surface 130 is formed adjacent a leading end137 of guide 124. Surface 130 is sized to slidably fit securely withinopen trailing end 98 (see FIGS. 13 and 16) of implant 10. Oncepositioned over surface 130 and against a receiving shelf 134, implant10 is locked onto guide 124 by outwardly biasing a pair of retainingpins 140 and 142 within tool fenestrations 114. Preferably, pins 140 and142 are sized sufficiently to fit within tool fenestrations 144, but areoversized relative to fenestrations 112 (of FIGS. 12-17). Hence, pins140 and 142 are sized to prevent misaligned mounting of implant 10 ontoinsertion tool 120.

[0088] More particularly, driver 122 forms a driver pin 156 that extendswithin an enlarged bore 136 formed within guide 124. Bore 136 decreasesin size immediately adjacent leading end 137 so as to form a reduceddiameter bore 132. Bore 132 enables clearance of a beveled frustoconicalend 148 of driver pin 156 during threaded adjustment between driver 122and guide 124. Frustoconical end 148 mates in sliding engagement with aradially inwardly extending end of each pin 140 and 142. Such inward endof each pin 140 and 142 forms a complementary beveled end that mates forsliding engagement with end 148 as driver 122 is adjustably positionedwithin guide 124.

[0089] Pins 140 and 142 are retained for radially extendinginward/outward movement within associated guide holes 144 and 146,respectively. More particularly, each pin 140 and 142 is retained withinhole 144 and 146 via a press-fit rolled pin 141 and 143, respectively.Each rolled pin 141 and 143 passes through an elongated slot formedthrough each associated pin 141 and 143. In this manner, each pin 141and 143 is allowed to slide within guide hole 144 and 146, respectively,but is prevent from becoming completely dislodged.

[0090] In order to facilitate insertion of implant 10, driver 122 has anenlarged driver handle 152 that terminates to form a driver end 154.Driver end 154 is shaped to facilitate impact with a hammer duringinsertion of an implant 10 between bone bodies. Furthermore, pins 140and 142 cooperate with recessed mounting surface 130 and shelf 134 torigidly and securely retain implant 10 on tool 120, even whereconsiderable lateral loading might occur. Such lateral loading mightoccur, for example, as a result of wiggling implant 10 and tool 120while attempting to insert tool 10 within a pair of prepared vertebrae.Upon insertion, implant 10 traps adjacent vertebrae for immediatefixation, within open leading end 96.

[0091] Once implant 10 has been inserted between bone bodies, nuts 126and 128 are loosened, after which driver 122 is loosened or unthreadedrelative to guide 124 which enables pins 140 and 142 to retract.Preferably, the outermost ends of pins 140 and 142 are chamfered tofacilitate removal of implant 10 from tool 120. Optionally,frustoconical end 148 can be magnetized to impart retraction of pins 140and 142 as drive pin 156 is retracted within guide 124.

[0092]FIGS. 19 and 20 illustrate prepared vertebrae 12 and 14 prior toinsertion of an implant and after insertion of an implant of Applicant'sinvention, respectively, but with the implant omitted for clarity. FIG.21 corresponds with FIG. 20, but shows the details of implant 10inserted in interlocking relation with vertebrae 12 and 14.

[0093] As shown in FIG. 19, a pair of vertebrae 12 and 14 are retainedtogether with an intervertebral disc 20. An aperture 18 is formedpartially as a kerf 44, and generates bone beds in the form of innersurfaces 160, 164 and outer surfaces 162, 166. A pair of intact boneprojections 168 and 170 are formed as a result extending from vertebrae12 and 14, respectively. Such bone projections 168 and 170 are entrappedwithin the open leading end 96 of implant 10 (see FIG. 12) immediatelyupon insertion. Hence, instant fixation is provide upon implant of suchdevice. Furthermore, instant distraction is also generated as a resultof the oblique outer surface 90 of implant 10 (see FIG. 12).

[0094] As shown in FIG. 20, the forcible insertion of an implant betweenbone bodies, or vertebrae, 12 and 14 causes self-distraction of amount“D” which corresponds to the difference in diameter for cylindricalleading edge 86 and the outermost dimension of oblique surface 90 alongthe vertical direction, as shown in FIG. 15. Dimension “D” is shownslightly exaggerated in FIG. 20 to more clearly illustrate theself-distraction feature. In most applications, a lumbar placement wouldgenerate approximately 5 millimeters of distraction distance “D”.

[0095]FIG. 21 illustrates implant 10 inserted into vertebrae 12 and 14.Due to the difference in wall thickness caused by the oblique outersurface and cylindrical inner surface of implant 10, cylindrical kerf 44only receives implant 10 snugly at the 12 o'clock (superior) and 6o'clock (inferior) positions as shown in FIG. 21. Tabs 116 are alsoshown inserted into vertebrae 12 and 14 which ensures retention ofimplant 10 therein, following implantation. Furthermore, the obliqueouter surface mates in conforming engagement with the prepared bone bedsin vertebrae 12 and 14 such that lateral bending and rotation isresisted due to the increased frictional forces caused by close fit-up,and due to non-cylindrical mating contact.

[0096] As shown in FIG. 21, implant 10 generates self-distractionbetween vertebrae 12 and 14, once implanted. The annulus is therebyplaced on stretch which further stabilizes instant fixation. Thenon-cylindrical fit-up between implant 10 and vertebrae 12 and 14cooperates with the stretched annulus so as to impart rigid, instantfixation. Furthermore, implant 10 stops further compression fromoccurring between vertebrae 12 and 14. Likewise, implant 10 entraps boneprojections 168 and 170, which prevents any distraction from occurringbetween vertebrae 12 and 14.

[0097]FIG. 22 shows implant 10 during implantation between vertebrae 12and 14, in a self-distracted position. Bone projections 168 and 170 areclearly shown entrapped within implant 10, which generates immediateentrapment of projections 168 and 170, and fixation between vertebrae 12and 14. After removal and retraction of tool 124, bone grafts, ormorsels, 172 are then packed inside of implant 10, as shown in FIG. 23.

[0098] According to FIG. 23, bone grafts 172 facilitate earlier boneingrowth and through growth. Similarly, fenestrations, as well as theopen leading and trailing ends, of implant 10 further facilitate suchingrowth and through growth.

[0099]FIG. 24 illustrates staged stabilization and fusion via Wolff'slaw, wherein bone remodeling and reorganization has further fixed andfused such adjacent vertebrae 12 and 14. The trabeculae relocate throughfenestrations to form a mature strengthening of the trabeculae.Additional reorganization is provided by preparing bone beds that recessimplant 10 within vertebrae, and by providing bone graft materialthereabout at the time of implantation. Accordingly, additional bone 8reorganization is facilitated outside of implant 10.

[0100]FIG. 24 is a sagittal section and diagrammatic view throughimplant 10 and vertebrae 12 and 14, illustrating reorganization of fusedbone material through implant 10. Histologic bone cell geometry is shownin greater detail, corresponding in time with complete bone remodeling.Lacunae and canals or voids 172 are formed between the bone 174.

[0101]FIG. 25 is a coronal and diagrammatic view taken perpendicular tothe view of FIG. 24 along line 25-25. In such view, bone cells haveremodeled to form a definite elongated configuration extending betweenvertebrae 12 and 14. Such remodeled bone through growth can be seenbetween fenestrations on some sides of a patient, occurring fromcephalad to caudad, as well as between fenestrations along a diagonalconfiguration of the patient, from cephalad to caudad.

[0102]FIGS. 26 and 27 illustrate an alternative embodimentself-distracting and fixating implant 210. FIG. 26 illustrates implant210 in perspective view. Implant 210 is constructed similarly to implant10 depicted in FIG. 12. However, implant 210 is provided with acylindrical outer surface 290 containing at least one helical thread291. Implant 210 has a cylindrical leading edge 286 and a cylindricaltrailing edge 288. Cylindrical outer surface 290 and a cylindrical innersurface 292 are formed between edges 286 and 288. A central cylindricalchamber, or aperture, 294 (see FIG. 27) is formed within implant 210,between edges 286 and 288. Chamber 294 forms an open leading end 296 andan open trailing end 298 within implant 210. Upon implantation, openleading end 296 entraps bone projections similar to those shown in FIGS.21 and 22 on implant 10. Accordingly, instant fixation is providedbetween vertebral bodies.

[0103] Also shown in FIGS. 26 and 27, a plurality of interruptions 202are formed in cylindrical leading edge 286, and extending into a taperedportion 204. Individual tapered fingers 200 are formed by interruptions202, along cylindrical leading edge 286. Interruptions 202 serve tocollect debris similar to the interruptions depicted for implant 10 ofFIG. 12.

[0104] Although implant 210 does not include an oblique outer surface, atapered portion 104 extends along leading edge 286 so as to impart adegree of distraction when inserted into the cylindrical kerf 44, shownin FIG. 20. However, the cylindrical threaded outer surface 290 will notgenerate quite the same degree of distraction, and will not impart thesame degree of fit-up as will implant 10 of FIG. 21.

[0105] Implant 210 also includes tool fenestrations 214 for facilitatinginsertion with tool or instrument 120 of FIG. 18. Furthermore, implant210 includes a plurality of fenestrations 212 for facilitating bonyingrowth and through growth following insertion of implant 210 withinbone bodies of adjacent vertebral bodies.

[0106] In compliance with the statute, the invention has been describedin language more or less specific as to structural and methodicalfeatures. It is to be understood, however, that the invention is notlimited to the specific features shown and described, since the meansherein disclosed comprise preferred forms of putting the invention intoeffect. The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. A bone joining implant, comprising; a tubularbody having an open leading end and a central aperture, the centralaperture similarly sized to the open leading end; the open leading endcommunicating with the central aperture and configured to entrap a boneprojection from each of a pair of adjacent bone bodies being joinedtogether.
 2. The implant of claim 1 wherein the tubular body has anoblique outer surface, a cylindrical inner surface, a cylindricalleading edge, and a tapered leading end portion, the tapered leading endportion extending from the cylindrical leading edge to the oblique outersurface.
 3. The implant of claim 1 further comprising a plurality ofretaining tabs provided on an outer surface of the tubular body andconfigured to retain the implant between the pair of adjacent bonebodies.
 4. The implant of claim 1 further comprising a plurality offenestrations provided in the tubular body, extending from the centralaperture to an outer surface.
 5. The implant of claim 1 wherein thetubular body has an open trailing end, the open leading end, the opentrailing end and the central aperture have a common, substantiallyuniform inner diameter configured to facilitate axial x-ray analysis ofarthrodesis.
 6. The implant of claim 1 wherein the tubular body has anopen trailing end, the central aperture communicating with the opentrailing end.
 7. The implant of claim 6 further comprising a pair oftool fenestrations provided adjacent the open trailing end andconfigured to enable mating of the implant with a tool during insertion.8. The implant of claim 6 wherein the tubular body includes at least oneguide slot provided within the open trailing end, the guide slotoperative to facilitate visual placement of the tubular body between apair of adjacent bone bodies.
 9. A vertebral interbody implant,comprising; a tubular body having an oblique outer surface, acylindrical inner surface, and a tapered portion extending from acylindrical leading end between the inner surface and the outer surface;the cylindrical leading end sized to be received within bone beds ofadjacent vertebrae being joined, and the tapered portion operative toself-distract the vertebrae during insertion of the oblique outersurface therebetween.
 10. The implant of claim 9 wherein an open leadingend is formed within the cylindrical leading end.
 11. The implant ofclaim 9 wherein the body includes an open leading end and an opentrailing end, a cylindrical aperture further being providedtherebetween.
 12. The implant of claim 9 further comprising a pluralityof fenestrations provided in the body, extending from the hollow portionto the oblique outer surface.
 13. The implant of claim 9 furthercomprising at least one tab carried by the oblique outer surface andconfigured for forcible engagement with a bone bed of an adjacentvertebra, the tab operative to retain the tubular body in securementwith the bone bed.
 14. The implant of claim 9 further comprising atleast one guide slot provided along a trailing end.
 15. The implant ofclaim 9 wherein the implant comprises a vertebral interbody fusingdevice.
 16. The implant of claim 9 further comprising a hollow portionprovided in the body, the hollow portion configured to receive bonegraft material therein, and a plurality of fenestrations provided in thebody, extending from the inner surface to the outer surface.
 17. Theimplant of claim 9 further comprising a hollow portion provided in thetubular body, the hollow portion configured to receive bone graftmaterial therein, and a plurality of fenestrations provided in the body,extending from the hollow portion to the outer surface, thefenestrations configured to promote physiological implant fixation. 18.A vertebral interbody implant, comprising: a tubular body having an openleading end, an open trailing end, and a central aperture, the centralaperture sized similarly to the open leading end and the open trailingend; the open leading end and the central aperture configured to entrapan integrally formed bone projection from each of a pair of adjacentbone bodies being joined together, the open leading end, open trailingend, and central aperture further cooperating to facilitate axial x-rayanalysis of arthrodesis following implantation.
 19. The implant of claim18 wherein the tubular body has an oblique outer surface.
 20. Theimplant of claim 19 wherein the tubular body has a cylindrical innersurface.
 21. The implant of claim 20 wherein the tubular body has atapered portion extending from the cylindrical leading end between theinner surface and the outer surface.
 22. A method for joining togethervertebral bodies, comprising: providing a tubular intervertebral implanthaving an open leading end communicating with a central aperture;preparing a receiving bed in each of a pair of adjacent vertebral bodiesseparated by an intervertebral disk, the vertebral bodies cooperating toform a cylindrical kerf, the kerf forming a bone projection from eachvertebral body; instantly fixing the vertebral bodies together byreceiving the tubular implant within the kerf such that adjacent boneprojections of associated vertebral bodies are received within the openleading end and into the central aperture.
 23. The method of claim 22wherein over time, the instantly fixed vertebral bodies fuse togethervia arthrodesis.
 24. The method according to claim 22 wherein thetubular body has an oblique outer surface, the oblique outer surfaceoperative to impart distraction when receiving the tubular implantwithin the cylindrical kerf.
 25. The method of claim 22 wherein thetubular body includes a plurality of tabs carried on an outer surface,each tab operable to engage with one of the receiving beds such that theimplant is immovably received within the cylindrical kerf.
 26. Themethod according to claim 22 wherein the tubular intervertebral implanthas an open leading end, an open trailing end, and a central aperture,the open trailing end, the open leading end and the central aperturehaving a substantially uniform inner diameter operative to facilitateaxial x-ray analysis of arthrodesis, wherein the implant is receivedwithin the kerf so as to facilitate x-ray analysis of arthrodesis. 27.The method of claim 26 wherein the tubular implant is positioned in agenerally anterior/posterior direction.
 28. The method of claim 22wherein each bone projection comprises intact bone formed integrallyfrom one of the vertebral bodies and configured to enhance osteogenesis.